Softening of fused-silica capillaries during particle packing

When a semipreparative capillary electrochromatography (CEC) capillary is p acked with silica particles and exposed to solvent, its mechanical strength is markedly reduced. In our studies, a fused-silica capillary (internal di ameter > 200 mu m and wall thickness < 150 mu m) was packed under pressure (approximately 200 psi) with spherical silica particles (1.5-5 mu m) suspen ded in water or various common organic solvents. After one hour of exposure , the capillary can be readily deformed, and it keeps its deformed shape up on release of the force causing deformation. It is suggested that capillary softening is promoted through the propagation of internal microcracks that have been caused by action of the particles during packing in the presence of solvent. Application of a protective coating to the inside of the capil lary is found to reduce or eliminate capillary softening.